U.S. patent number 9,057,679 [Application Number 13/756,211] was granted by the patent office on 2015-06-16 for combined scatter and transmission multi-view imaging system.
This patent grant is currently assigned to Rapiscan Systems, Inc.. The grantee listed for this patent is Rapiscan Systems, Inc.. Invention is credited to Edward James Morton.
United States Patent |
9,057,679 |
Morton |
June 16, 2015 |
Combined scatter and transmission multi-view imaging system
Abstract
The present specification discloses a multi-view X-ray
inspection system having, in one of several embodiments, a
three-view configuration with three X-ray sources. Each X-ray
source rotates and is configured to emit a rotating X-ray pencil
beam and at least two detector arrays, where each detector array
has multiple non-pixellated detectors such that at least a portion
of the non-pixellated detectors are oriented toward both the two
X-ray sources.
Inventors: |
Morton; Edward James
(Guildford, GB) |
Applicant: |
Name |
City |
State |
Country |
Type |
Rapiscan Systems, Inc. |
Torrance |
CA |
US |
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Assignee: |
Rapiscan Systems, Inc.
(Torrance, CA)
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Family
ID: |
48905841 |
Appl.
No.: |
13/756,211 |
Filed: |
January 31, 2013 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20140044233 A1 |
Feb 13, 2014 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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61594625 |
Feb 3, 2012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01V
5/0016 (20130101); G01V 5/0033 (20130101); G01V
5/0008 (20130101); G01N 23/04 (20130101); G01V
5/0025 (20130101); G21K 1/043 (20130101); G01V
5/0075 (20130101); G01N 23/20008 (20130101); G01N
23/20083 (20130101); G01V 5/0066 (20130101); H05G
1/70 (20130101); G01N 2201/10 (20130101); G01N
2201/1047 (20130101) |
Current International
Class: |
G01N
23/087 (20060101); G01V 5/00 (20060101); H05G
1/70 (20060101); G01N 23/04 (20060101); G01N
23/203 (20060101) |
Field of
Search: |
;378/57,62,86-92,95,98.8,119,121,146,147,149-151,204,210
;250/370.01,370.08,370.09,370.1,370.11,370.12,370.13,370.14,374,382,487.1 |
References Cited
[Referenced By]
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WO |
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Aug 2013 |
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WO |
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Other References
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PCT/US2010/041757, Oct. 12, 2010. cited by applicant .
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cited by applicant .
European Patent Office Summons to attend oral proceedings pursuant
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May 6, 2009, 3 pages. cited by applicant .
European Patent Office, International Search Report and Written
Opinion of the International Searching Authority,
PCT/US2005/011382, Oct. 21, 2005. cited by applicant .
European Patent Office, International Search Report, International
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by applicant .
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Primary Examiner: Midkiff; Anastasia
Attorney, Agent or Firm: Novel IP
Parent Case Text
CROSS-REFERENCE
The present application relies on U.S. Patent Provisional
Application No. 61/594,625, filed on Feb. 3, 2012 for priority. The
aforementioned application is herein incorporated by reference.
Claims
I claim:
1. An X-ray inspection system for scanning an object, the
inspection system comprising: a first X-ray source and a second
X-ray source, each configured to simultaneously emit rotating X-ray
beams for irradiating the object, wherein each of said X-ray beams
defines a transmission path; a detector array comprising at least
one transmission detector placed between at least two backscatter
detectors, wherein each of said backscatter detectors detects
backscattered X-rays emitted by the first X-ray source placed on a
first side of the object and wherein the transmission detectors
detects transmitted X-rays emitted by the second X-ray source
placed on an opposing side of the object; and at least one
controller for controlling each of the first and second X-ray
sources to concurrently scan the object in a coordinated,
non-overlapping, manner such that the transmission paths of each of
said X-ray beams does not cross.
2. The X-ray inspection system as claimed in claim 1 wherein the
detector array comprises at least two rectangular profile
backscatter detectors and a square profile transmission detector
positioned between said at least two rectangular profile
backscatter detectors.
3. The X-ray inspection system as claimed in claim 1 wherein the
detector array comprises a transmission detector positioned between
two backscatter detectors and wherein the detectors are placed
within a single plane facing the object begin scanned and the
transmission detector has a smaller exposed surface area than each
of the backscatter detectors.
4. The X-ray inspection system as claimed in claim 1 further
comprising a pair of fixed collimators positioned between the
transmission detector and one of said at least two backscatter
detectors.
5. The X-ray inspection system as claimed in claim 1 wherein each
of the X-ray sources comprises an extended anode X-ray tube, a
rotating collimator assembly, a bearing, a drive motor, and a
rotary encoder.
6. The X-ray inspection system as claimed in claim 1 wherein each
of the first and second X-ray sources comprises: an extended anode
X-ray tube coupled with a cooling circuit, the anode being at
ground potential; a rotating collimator assembly comprising at
least one collimating ring with slots cut at predefined angles
around a circumference of the collimator, a length of each slot
being greater than a width and an axis of rotation of the slot, and
the width of the slots defining an intrinsic spatial resolution of
the X-ray inspection system in a direction of the scanning; a
bearing for supporting a weight of the collimator assembly and
transferring a drive shaft from the collimator assembly to a drive
motor; a rotary encoder for determining an absolute angle of
rotation of the X-ray beams; and a secondary collimator set for
improving spatial resolution in a perpendicular scanning
direction.
7. The X-ray inspection system as claimed in claim 6 wherein the
controller receives speed data comprising a speed of the object
and, based upon said speed data, adjusts at least one of a
collimator rotation speed of an X-ray source, a data acquisition
rate, or an X-ray tube current based upon said speed data.
Description
FIELD OF THE INVENTION
The present specification relates generally to the field of X-ray
imaging system for security scanning and more specifically to
multi-view X-ray scanning systems that advantageously combine
transmission and backscatter imaging.
BACKGROUND
With the proliferation of terrorism and contraband trade, there
exists an imminent need for systems that can effectively and
efficiently screen cars, buses, larger vehicles and cargo to detect
suspicious threats and illegal substances.
In the past, many technologies have been assessed for use in
security inspection, and often X-ray imaging has been identified as
a reasonable technique for such purposes. Several known X-ray
scanning systems have been deployed for screening cars, buses and
other vehicles. Such systems include transmission and backscatter
X-ray screening systems. These prior art X-ray systems provide
scanning from a very limited number of orientations, typically one
and potentially two. For example, a transmission X-ray system may
be configured in a side-shooter or top-shooter configuration.
Backscatter systems may be available in single sided or,
occasionally, in a three sided configuration.
Accordingly, there is need in the prior art for a multi-view
imaging system which can have an arbitrary number of views, and
typically more than one. There is also need in the art for a
modular multi-view system that results in high detection
performance at very low dose using a combination of backscatter and
transmission imaging methodologies.
SUMMARY OF THE INVENTION
The present specification discloses, in one embodiment, an X-ray
inspection system comprising an X-ray source configured to emit an
X-ray beam; and a detector array comprising a plurality of
non-pixellated detectors, wherein at least a portion of said
non-pixellated detectors are not oriented toward the X-ray
source.
In another embodiment, the present specification discloses an X-ray
inspection system comprising at least two X-ray sources, wherein
each X-ray source is configured to emit an X-ray beam; and at least
two detector arrays, wherein each detector array comprises a
plurality of non-pixellated detectors, wherein at least a portion
of said non-pixellated detectors are oriented toward both X-ray
sources.
In yet another embodiment, the present specification discloses a
multi-view X-ray inspection system having a three-view
configuration comprising three X-ray sources, wherein each X-ray
source rotates and is configured to emit a rotating X-ray pencil
beam; and at least two detector arrays, wherein each detector array
comprises a plurality of non-pixellated detectors, wherein at least
a portion of said non-pixellated detectors are oriented toward both
X-ray sources.
In an embodiment, the X-ray beam is a pencil beam and each X-ray
source rotates over an angle of rotation, and the X-ray inspection
system has an intrinsic spatial resolution and wherein said
intrinsic spatial resolution is determined by a degree of
collimation of the X-ray beam and not by a degree of pixellation of
X-ray scan data. Further, in an embodiment, a single detector is
exposed to only one X-ray beam from one of said X-ray sources at a
specific point in time, and each detector defines a plane and
wherein said plane is offset from each plane defined by each X-ray
source. In an embodiment, each detector has a rectangular
shape.
In another embodiment of the present invention, the X-ray
inspection system comprises at least one X-ray source configured to
emit an X-ray beam; and a detector array comprising at least two
rectangular profile backscatter detectors and a square profile
transmission detector positioned between said at least two
rectangular profile backscatter detectors.
In yet another embodiment, the present specification discloses an
X-ray inspection system comprising at least one X-ray source
configured to emit an X-ray beam; and a detector array comprising
at least two rectangular profile backscatter detectors, a square
profile transmission detector positioned between said at least two
rectangular profile backscatter detectors, and a pair of fixed
collimators positioned between the square profile transmission
detector and one of said at least two rectangular profile
backscatter detectors.
In an embodiment, an X-ray inspection system comprising a control
system wherein, when said X-ray inspection system is activated to
detect gamma rays, said control system turns off an X-ray source
and switches a detector data processing mode from current
integrating mode to a pulse counting mode, is disclosed.
In another embodiment, the present invention discloses an X-ray
inspection system having at least one X-ray source, wherein said
X-ray source comprises an extended anode X-ray tube, a rotating
collimator assembly, a bearing, a drive motor, and a rotary
encoder.
In yet another embodiment, the present invention discloses, an
X-ray inspection system having at least one X-ray source, wherein
said X-ray source comprises an extended anode X-ray tube, a
rotating collimator assembly, a bearing, a drive motor, a secondary
collimator set, and a rotary encoder.
In an embodiment, an X-ray inspection system comprising a control
system wherein said control system receives speed data and wherein
said control system adjusts at least one of a collimator rotation
speed of an X-ray source, data acquisition rate, or X-ray tube
current based upon said speed data, is disclosed.
In another embodiment, the present specification discloses an X-ray
inspection system comprising a control system wherein said control
system adjusts at least one of a collimator rotation speed of an
X-ray source, data acquisition rate, or X-ray tube current to
ensure a uniform dose per unit length of an object being
scanned.
The present specification is also directed toward an X-ray
inspection system for scanning an object, the inspection system
comprising: at least two rotating X-ray sources configured to
simultaneously emit rotating X-ray beams, each of said X-ray beams
defining a transmission path; at least two detector arrays, wherein
each of said at least two detector arrays is placed opposite one of
the at least two X-ray sources to form a scanning area; and at
least one controller for controlling each of the X-ray sources to
scan the object in a coordinated manner, such that the X-ray beams
of the at least two X-ray sources do not cross transmission
paths.
In one embodiment, each of the emitted X-ray beams is a pencil beam
and each X-ray source rotates over a predetermined angle of
rotation.
In one embodiment, each detector is a non-pixellated detector.
In one embodiment, a first, a second and a third rotating X-ray
sources are configured to simultaneously emit rotating X-ray beams,
wherein the first X-ray source scans the object by starting at a
substantially vertical position and moving in a clockwise manner;
wherein the second X-ray source scans the object by starting at a
substantially downward vertical position and moving in a clockwise
manner; and wherein the third X-ray source scans the object by
starting at a substantially horizontal position and moving in a
clockwise manner.
In one embodiment, the controller causes each X-ray source to begin
scanning the object in a direction that does not overlap with an
initial scanning direction of any of the remaining X-ray sources,
thereby eliminating cross talk among the X-ray sources.
In one embodiment, a plurality of scanned views of the object are
collected simultaneously with each detector being irradiated by no
more than one X-ray beam at any one time.
In one embodiment, a volume of the detectors is independent of a
number of scanned views of the object obtained.
In one embodiment, the X-ray inspection system has an intrinsic
spatial resolution wherein said intrinsic spatial resolution is
determined by a degree of collimation of an X-ray beam.
In one embodiment, the one or more detectors comprise an array of
scintillator detectors having one or more photomultiplier tubes
emerging from an edge of the detector array to allow X-ray beams
from adjacent X-ray sources to pass an unobstructed face of the
detector array opposite to the photomultiplier tubes.
In one embodiment, the one or more detectors are formed from a bar
of a scintillation material that has a high light output
efficiency, a fast response time and is mechanically stable over
large volumes with little response to changing environmental
conditions.
In one embodiment, the one or more detectors are gas ionization
detectors comprising a Xenon or any other pressurized gas.
In one embodiment, the one or more detectors are formed from a
semiconductor material such as but not limited to CdZnTe, CdTe,
HgI, Si and Ge.
In one embodiment, the X-ray inspection system is configured to
detect gamma rays by turning off the X-ray sources switching the
detectors from a current integrating mode to a pulse counting
mode.
The present specification is also directed toward an X-ray
inspection system for scanning an object, the inspection system
comprising: at least two X-ray sources configured to simultaneously
emit rotating X-ray beams for irradiating the object, wherein each
of said X-ray beams defines a transmission path; a detector array
comprising at least one transmission detector placed between at
least two backscatter detectors, wherein each of said backscatter
detectors detects backscattered X-rays emitted by a first X-ray
source placed on a first side of the object and wherein the
transmission detectors detects transmitted X-rays emitted by a
second X-ray source placed on an opposing side of the object; and
at least one controller for controlling each of the X-ray sources
to concurrently scan the object in a coordinated, non-overlapping,
manner such that the transmission paths of each of said X-ray beams
does not cross.
In one embodiment, the detector array comprises at least two
rectangular profile backscatter detectors and a square profile
transmission detector positioned between said at least two
rectangular profile backscatter detectors.
In another embodiment, the detector array comprises a transmission
detector positioned between two backscatter detectors wherein the
detectors are placed within a single plane facing the object begin
scanned and the transmission detector has a smaller exposed surface
area than each of the backscatter detectors.
In one embodiment, the X-ray inspection system further comprises a
pair of fixed collimators positioned between the transmission
detector and one of said at least two backscatter detectors.
In one embodiment, each of the X-ray sources comprises an extended
anode X-ray tube, a rotating collimator assembly, a bearing, a
drive motor, and a rotary encoder.
In another embodiment, each of the X-ray sources comprises: an
extended anode X-ray tube coupled with a cooling circuit, the anode
being at ground potential; a rotating collimator assembly
comprising at least one collimating ring with slots cut at
predefined angles around a circumference of the collimator, a
length of each slot being greater than a width and an axis of
rotation of the slot, and the width of the slots defining an
intrinsic spatial resolution of the X-ray inspection system in a
direction of the scanning; a bearing for supporting a weight of the
collimator assembly and transferring a drive shaft from the
collimator assembly to a drive motor; a rotary encoder for
determining an absolute angle of rotation of the X-ray beams; and a
secondary collimator set for improving spatial resolution in a
perpendicular scanning direction.
In one embodiment, the controller receives speed data comprising a
speed of the object and, based upon said speed data, adjusts at
least one of a collimator rotation speed of an X-ray source, a data
acquisition rate, or an X-ray tube current based upon said speed
data.
The aforementioned and other embodiments of the present shall be
described in greater depth in the drawings and detailed description
provided below.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features and advantages of the present invention
will be appreciated, as they become better understood by reference
to the following detailed description when considered in connection
with the accompanying drawings:
FIG. 1 shows a single-view top-shooter transmission imaging system
in accordance with one embodiment of the present invention;
FIG. 2 is a first side-shooter configuration of one embodiment of
the present invention;
FIG. 3 is a second side-shooter configuration of one embodiment of
the present invention;
FIG. 4 is a multi-view X-ray imaging system embodiment of the
present invention;
FIG. 5 shows X-ray detector offset geometry from a plane of X-ray
sources for use in the multi-view X-ray imaging system of the
present invention;
FIG. 6 shows an embodiment of a suitable X-ray detector for use in
the multi-view system of the present invention;
FIG. 7a is a side view of a detector array for use in the
multi-view system of the present invention;
FIG. 7b is an end view of the detector array for use in the
multi-view system of the present invention;
FIG. 8 shows an embodiment of a backscatter-transmission detector
configuration for use with multi-view system of the present
invention;
FIG. 9 shows an alternate embodiment of the
backscatter-transmission detector configuration for use with
multi-view system of the present invention;
FIG. 10 shows an embodiment of a suitable scanning X-ray source for
use with multi-view system of the present invention;
FIG. 11a shows a secondary collimator set to improve spatial
resolution in the perpendicular direction;
FIG. 11b shows the secondary collimator set of FIG. 11a positioned
around an outer edge of a rotating collimator;
FIG. 12 shows an embodiment of read-out electronic circuit for use
with detectors of the multi-view system of the present
invention;
FIG. 13 shows a matrixed configuration where a set of `n`
multi-view imaging systems are monitored by a group of `m` image
inspectors;
FIG. 14 shows a deployment of a multi-view imaging system to scan
cargo, in accordance with an embodiment of the present
invention;
FIG. 15 shows a deployment of a multi-view imaging system to scan
occupied vehicles in accordance with an embodiment of the present
invention;
FIG. 16a shows a mobile inspection system in its operating state
ready for scanning;
FIG. 16b shows the step of folding up of vertical boom about a
hinge point at the end of horizontal boom;
FIG. 16c shows the step of folding up the horizontal boom and,
concurrently, the vertical boom around a hinge point at the top of
a vertical support;
FIG. 16d shows the step of laying down the vertical boom toward the
back of the mobile inspection vehicle;
FIG. 16e shows the step of folding up the bottom imaging section by
at least 90 degrees from its operating position;
FIG. 16f shows the step of folding an outer horizontal base section
by 180 degrees to cause it to lie parallel to inner base section;
and
FIG. 16g shows the step of completely folding the base section by
90 degrees to complete the system stow.
DETAILED DESCRIPTION OF THE INVENTION
The present specification is directed towards an X-ray scanning
system that advantageously combines image information from both
backscatter and transmission technologies. More specifically, the
present invention employs four discrete backscatter systems,
however re-uses the pencil beam from one backscatter system to
illuminate large area detectors from a second backscatter system so
that simultaneous multi-sided backscatter and transmission imaging
using the same set of four X-ray beams can be achieved. This
approach is cost effective, in that it saves the cost of a
segmented detector array yet still provides a comprehensive
inspection.
The present specification is directed towards multiple embodiments.
The following disclosure is provided in order to enable a person
having ordinary skill in the art to practice the invention.
Language used in this specification should not be interpreted as a
general disavowal of any one specific embodiment or used to limit
the claims beyond the meaning of the terms used therein. The
general principles defined herein may be applied to other
embodiments and applications without departing from the spirit and
scope of the invention. Also, the terminology and phraseology used
is for the purpose of describing exemplary embodiments and should
not be considered limiting. Thus, the present invention is to be
accorded the widest scope encompassing numerous alternatives,
modifications and equivalents consistent with the principles and
features disclosed. For purpose of clarity, details relating to
technical material that is known in the technical fields related to
the invention have not been described in detail so as not to
unnecessarily obscure the present invention.
FIG. 1 shows a single-view top-shooter transmission imaging system
100 in accordance with an embodiment of the present invention.
System 100 comprises an X-ray source 105 with a rotating pencil
beam collimator. When the X-ray beam is on, the collimator rotates
continuously to form a moving X-ray beam 110 that sweeps over a
fan-shaped area 115. A series of X-ray detectors 120 are placed in
a transmission inspection geometry, namely opposite the X-ray beam
110 and with the inspected object between the detectors 120 and
X-ray beam 110, to record the intensity of the X-ray beam 110 once
it has passed through object 125, such as a vehicle. In one
embodiment, detectors 120 are on the order of 1000 mm long and
stacked end-to-end to form a linear sensor having a length equal to
a plurality of meters. An advantage of such detectors is that they
can be fabricated quite inexpensively, since they do not have
spatial resolution.
An X-ray scan image, of the object 125, is formed by recording
intensity of signal at output of each detector 120 at all times, as
well as the angle of rotation of the X-ray pencil beam 110. In
radial coordinates, object X-ray transmission is determined by
plotting the recorded X-ray intensity from X-ray detectors 120
which is being pointed to by the X-ray beam 110 against its angle
of rotation at any given instant. As known to persons of ordinary
skill in the art a predetermined coordinate transform maps this
data back onto a Cartesian grid or any other chosen co-ordinate
grid.
In contrast to typical prior art X-ray imaging systems, the
intrinsic spatial resolution of the system 100 is determined not by
pixellation of the X-ray scan data but by collimation of the X-ray
beam 110 at the source 105. Since the X-ray beam 110 is produced
from a small focal spot with finite area, the X-ray pencil beam 110
is diverging and therefore the spatial resolution of the system 100
varies with distance of the detectors 120 from the source 105.
Therefore, spatial resolution of the system 100 is least in the
lower corners directly opposite to the X-ray source 105. However,
this varying spatial resolution is corrected by deconvolution of
the spatial impulse response of the system 100 as a function of
rotation angle to thereby produce an image with constant
perceptible spatial resolution.
FIG. 2 is a side-shooter configuration, of the system 100 of FIG.
1, that uses a similar identical X-ray source 205 with a rotating
pencil beam 210 and a series of identical X-ray detectors 220 but
in alternative locations. As shown in FIG. 3, a mirrored
side-shooter configuration is achieved using the same X-ray source
305 and detectors 320 but in a mirror image configuration to that
shown in FIG. 2.
FIG. 4 is a multi-view X-ray imaging system 400 that integrates the
configurations of FIGS. 1 through 3 in accordance with an
embodiment of the present invention. In one embodiment, system 400
has a three-view configuration enabled by three simultaneously
active rotating X-ray beams 405, 406 and 407 with plurality of
detectors placed correspondingly, in one embodiment, in
transmission configuration to form a scanning tunnel 420. System
400 provides a high degree of inspection capability, in accordance
with an object of the present invention, while at the same time
achieving this at substantially low X-ray dose since the volume of
space irradiated at any moment in time is low compared to
conventional prior art line scan systems that typically have large
numbers of pixellated X-ray detectors and fan-beam X-ray
irradiation.
As shown in FIG. 4, there is almost no cross talk between the three
X-ray views which are collected simultaneously because the X-ray
sources 405, 406, 407, are controlled by at least one controller
497, which may be local to or remote from the X-ray sources 405,
406, 407, that transmits control signals to each X-ray source 405,
406, 407 in a manner that causes them to scan the target object 495
in a coordinated, and non-overlapping, manner. In one embodiment,
X-ray source 405 scans object 495 by starting at a substantially
vertical position (between 12 o'clock and 1 o'clock) and moving in
a clockwise manner. Concurrently, X-ray source 406 scans object 495
by starting at a substantially downward vertical position (around 4
o'clock) and moving in a clockwise manner. Concurrently, X-ray
source 407 scans object 495 by starting at a substantially
horizontal position (around 9 o'clock) and moving in a clockwise
manner. It should be appreciated that each of the aforementioned
X-ray sources could begin at a different position, provided that a)
each starts a scan in a direction that does not overlap with the
initial scanning direction of the other X-ray sources and b) each
scans in a direction and at a speed that does not substantially
overlap with the scan of the other X-ray sources.
According to an aspect of the present invention, there is almost no
limit to the number of views which may be collected simultaneously
in the system 400 with each detector segment 421 being irradiated
by no more than one primary X-ray beam at any one time. In one
embodiment, the detector configuration 430, shown in FIG. 4,
comprises 12 detector segments 421 each of approximately 1 m in
length to form an inspection tunnel of approximately 3 m
(Width).times.3 m (Height). In one embodiment, the detector
configuration 430 is capable of supporting six independent X-ray
views to allow transition of the sweeping X-ray views between
adjacent detectors. An alternate embodiment comprising 0.5 m long
detector segments 421 is capable of supporting up to 12 independent
X-ray image views.
Persons of ordinary skill in the art should appreciate that, in
system 400, the volume of detector material is independent of the
number of views to be collected and the density of readout
electronics is quite low compared to conventional prior art
pixellated X-ray detector arrays. Additionally, a plurality of
X-ray sources can be driven from a suitably rated high voltage
generator thereby enabling additional X-ray sources to be added
relatively simply and conveniently. These features enable the high
density multi-view system 400 of the present invention to be
advantageously used in security screening applications.
As shown in FIG. 5, a multi-view system, such as that shown in FIG.
4, has X-ray detectors 520 offset from the plane of the X-ray
sources 505. The offset prevents X-ray beams 510 from being
absorbed relatively strongly in the detector nearest to it, before
the beam can enter the object under inspection.
According to another aspect, X-ray detectors are not required to
have a spatial resolving function thereby allowing the primary beam
to wander over the face of the detector, and to a side face of the
detector, with minimal impact on overall performance of the imaging
system. This considerably simplifies the detector configuration in
comparison to a conventional prior art pixellated X-ray system,
since, in a pixellated system, each detector needs to be oriented
to point back towards a corresponding source to maintain spatial
resolution. Thus, in prior art pixellated X-ray systems, a single
detector cannot point to more than one source position and,
therefore, a dedicated pixellated array is needed for each source
point.
FIG. 6 shows an embodiment of a suitable X-ray detector 600 for use
in a multi-view system (such as the three-view system 400 of FIG.
4) of the present invention. As shown, detector 600 is formed from
a bar 605 of X-ray detection material, that in one embodiment is
fabricated from scintillation material. In a scintillation process,
X-ray energy is converted to optical photons and these photons are
collected using a suitable optical detector, such as a
photomultiplier tube or photodiode 610. Suitable scintillation
detection materials comprise plastic scintillators, CsI, BGO, NaI,
or any other scintillation material known to persons of ordinary
skill in the art that has high light output efficiency, fast time
response and is mechanically stable over large volumes with little
response to changing environmental conditions. Alternatively,
detector materials can also comprise gas ionisation and gas
proportional detectors, ideally with pressurised gas to enhance
detection efficiency and high electric field strengths for
improving signal collection times. Noble gas based detectors such
as pressurised Xenon detectors are quite suitable for use with the
multi-view system of present invention. Semiconductor detector
materials could also be adopted, such as CdZnTe, CdTe, HgI, Si and
Ge, although the capacitance, response time, costs and temperature
response of these materials make them a less preferred choice.
An array of scintillator detectors 720 is shown in FIGS. 7a and 7b
with photomultiplier tubes 725 emerging from the same long edge of
scintillating material to allow X-ray beams from adjacent X-ray
sources to pass the unobstructed face of the detector opposite to
the photomultiplier tubes 725. Two X-ray sources 705, 706 are
visible in the side view of the detector array 720 of FIG. 7a.
Three X-ray sources 705, 706, 707 are visible in the end view of
FIG. 7b.
From X-rays which are transmitted straight through an object and to
a set of transmission detectors on the opposite side of the object,
a fraction of the X-rays scatter from the object into other
directions. It is known to those of ordinary skill in the art that
the probability of detecting a scattered X-ray varies with the
inverse square of distance of the detector from the scattering
site. This means that a detector placed proximate to an X-ray beam,
as it enters the object, will receive a much larger backscatter
signal than a detector placed at significant distance from X-ray
source.
FIG. 8 shows an embodiment of a detector configuration for use with
multi-view system of the present invention to utilize X-rays
backscattered from an object under inspection, in addition to
transmitted X-rays. In this embodiment, an X-ray source 805
illuminates object 825 with a scanning pencil beam 810 of X-rays. A
fraction of the X-rays 815 backscatter, which are then sensed by a
pair of rectangular detectors 821, 822. Transmission X-ray beam 830
from a second X-ray source (not shown) at the other side of the
object 825, is captured at a smaller square section detector
835.
It should be noted herein that the detectors can be of any shape
and are not limited to a rectangular shape. In this particular
embodiment, a rectangular shape is selected because it produces a
uniform response and has a relatively manufacturing cost. In
addition, a rectangular shape is easier to stack end-to-end
compared with a circular or other curved detector. Similarly, using
a smaller square cross-section will most likely yield the most
uniform response, for example, when compared to a cylindrical
detector with a circular cross section, and is relatively lower in
cost to manufacture.
The square profile transmission detector 835 is placed between the
two rectangular profile backscatter detectors 821, 822. A pair of
fixed collimators 840 substantially reduces the effect of scattered
radiation on the transmission detector 835, resulting from a nearby
X-ray source, which measures relatively weak transmission signals
from the opposing X-ray source (not shown). All detectors 821, 822
and 835 are shielded using suitable materials, such as steel and
lead, around all faces except their active faces to avoid
background signal due to natural gamma-radiation and unwanted X-ray
scattering. Therefore, a transmission detector is sandwiched
between two backscatter detectors, within a single plane facing the
object begin scanned, and the transmission detector has a smaller
exposed surface area than each of the backscatter detectors.
FIG. 9 shows an alternate embodiment of combined X-ray
backscatter-transmission detectors. Here, a large imaging panel
900, which in one embodiment ranges from 1.5 m to 3.0 m in total
length, comprises six individual X-ray detectors in addition to a
scanning X-ray source 905. Four of the detectors 910, 911, 912 and
913 are used for recording X-ray backscatter from the local X-ray
source 905, while two detectors 914, 915 having smaller exposed
surface areas than each of the backscatter detectors 910, 911, 912,
913 are used to record transmission X-ray signals from an opposing
X-ray generator.
Persons of ordinary skill in the art should note that with the
detector configurations of FIGS. 8 and 9, a multi-view backscatter
system of the present invention is achieved that has one
backscatter view corresponding to each transmission view.
According to a further aspect, transmission imaging detectors can
also be used for recording backscatter signals when not being
directly irradiated by a transmission imaging beam. However, use of
additional detection sensors, as shown in FIGS. 8 and 9
substantially improve sensitivity of the backscatter detectors
albeit at substantially higher cost. Therefore, a low cost system
with modest backscatter performance can be assembled using just a
single detector array in offset geometry as shown in FIGS. 5 and
6.
In one embodiment, the additional backscatter imaging panels are
formed from a low cost high volume detector material such as
scintillation materials comprising plastic scintillators,
scintillation screens such as GdO.sub.2S with optical light guides,
and solid scintillators such as CsI and NaI although any
scintillator known to those of ordinary skill in the art may be
used, providing it has a fast response time (<10 us primary
decay time), good uniformity, and stability against change in
ambient conditions. Semiconductor and gas filled detectors may also
be used, although these are less preferred with the exception of
pressured Xenon gas detectors.
According to yet another aspect of the present invention, the large
area array of detector panels of FIGS. 8 and 9 are also used as
passive detectors of gamma radiation such as that emitted from
special nuclear materials and other radioactive sources of interest
such as Co-60, Cs-137 and Am-241. To enable system sensitivity to
passive gamma rays, the X-ray sources are turned off and the
detector electronics switched from a current integrating mode to a
pulse counting mode. The object, such as a vehicle, under
inspection is first scanned with the X-ray system of the present
invention. It should be noted herein that the method of the present
invention can be used in a single-view configuration or a
multi-view configuration. If a suspicious item is detected, the
vehicle is re-scanned, this time, in passive detection mode. This
provides dual operating function capability for the imaging system
of the present invention. Further, due to spatial positioning of
the detector panels, it is possible to approximately localize
radioactive source in space (recognizing the inverse square
reduction of count rate at detectors due to the distance of the
detector from the source). This localization is applied to the
multi-view X-ray images in the form of a graphic overlay to show
the position of a passive gamma source.
As shown in FIG. 10, an embodiment of a suitable scanning X-ray
source 1000, for use with multi-view system of the present
invention, comprises an extended anode X-ray tube 1005, a rotating
collimator assembly 1010, a bearing 1015, a drive motor 1020, and a
rotary encoder 1025.
In one embodiment, extended anode X-ray tube 1005 has the anode at
ground potential. The anode is provided with a cooling circuit to
minimize the thermal heating of the target during extended
operating periods. In one embodiment, a rotating collimator
assembly 1010 is advantageously formed from suitable engineering
materials such as steel and tungsten. The collimator comprises at
least one collimating ring with slots cut at appropriate angles
around circumference of the collimator. The length of each slot is
greater than its width and is longer than its axis of rotation and
narrow in the direction of rotation. Width of the slots defines
intrinsic spatial resolution of the transmission imaging system in
the direction of the scanning.
Bearing 1015 supports the weight of the collimator assembly 1010
and transfers a drive shaft from the collimator assembly to a drive
motor 1020. The drive motor 1020 is capable of being speed
controlled using an electronic servo drive to maintain exact speed
of rotation. A rotary encoder 1025 provides absolute angle of
rotation since this is required to determine the position of each
sampled detector point in the final generated image.
The rotating X-ray beam produced by the source 1000 of FIG. 10 has
good resolution in one dimension only. To improve spatial
resolution in the perpendicular direction, a secondary collimator
set is provided as shown in FIGS. 11a and 11b. Referring now to
FIGS. 11a and 11b simultaneously, hoop-like collimators 1100 are
placed around outer edge of the rotating collimator 1110 to provide
collimation into beam width direction. Since in one embodiment
transmission detectors are likely to be of a square section (such
as detectors 835 of FIG. 8) and. when combined with offset system
geometry of the present invention (as discussed with reference to
FIG. 5), use of a secondary beam width collimator 1110 allows a
specific shape of beam to be produced which precisely follows the
center line of the imaging detectors.
In an embodiment of the present invention, additional collimation
is placed at transmission detectors to constrain the width of X-ray
beam before it enters the detection material itself. This allows an
image of arbitrary spatial resolution to be collected even if an
actual X-ray beam passing through object is of lower intrinsic
spatial resolution. The width of the X-ray beam passing through the
object is kept as small as possible, but consistent with the final
collimator slot width, in order to minimise dose to the object
under inspection.
Each detector in the multi-view system is provided with readout
electronics which biases the photodetector, buffers and amplifies
output signal from the photodetector and digitizes the resulting
signal. FIG. 12 shows an embodiment of photomultiplier tube circuit
1205 with buffer amplifier and high speed analogue-to-digital (ADC)
converter 1210. Data from the ADC 1210 is transferred into a system
controller circuit 1215 along with digital data from all of the
other photodetectors (DET.sub.1, DET.sub.2, . . . , DET.sub.n). The
system controller 1215 also takes in encoder data 1220 from each of
X-ray sources and provides motor drive signals 1225 to each X-ray
source. Thus, the system controller 1215 coordinates data
acquisition between each component of the detector system and
generates an image data stream 1230 which provides data
individually for each transmission and backscatter X-ray view.
A set of suitable sensors 1235 are used to measure speed of the
vehicle or object under inspection as it passes through the
inspection region. Suitable sensors comprise microwave radar
cameras, scanning infra-red lasers or simply inductive sensors
placed at known distance apart which can provide a measurement of
speed (=distance/time) by comparing the times at which each sensor
goes from false to true and vice versa as the vehicle scans past.
This speed information, in one embodiment, is passed to the system
controller 1215 which then adjusts collimator rotation speed, data
acquisition rate and X-ray tube current to ensure a uniform dose
per unit length of the object being scanned. By using a high speed
ADC 1210, multiple samples are acquired at each transmission and
backscatter source point so that an average value, or otherwise
filtered value, is stored to improve signal-to-noise ratio of the
imaging system.
The linear scanning velocity of X-ray beams across the face of a
transmission imaging detector varies as a function of the distance
from the source (i.e., more distant points suffer a faster linear
scan rate). Therefore, in one embodiment, use of a high speed
oversampling analogue-to-digital converter 1210 simplifies the
adjustment of sample time to match the linear scanning velocity
using, for example, encoder data 1220 to trigger the start of each
sampling period, where the relevant encoder values are stored in a
digital lookup table prior to the start of scanning. Sampling of
data at a high speed allows for an improved deconvolution of the
spatial resolution in the scanning direction by oversampling the
measured data and generating a lower sample rate output image data
compared to that which would be achieved by trying to de-convolve
only a low sample rate image.
According to an embodiment, the system controller 1215 is
advantageously designed using a combination of digital electronics,
such as a field programmable gate array, and a microcontroller. The
digital circuits provide precise timing that is required to build
up a scanned image from multiple detectors and multiple encoders in
an automated fashion, using only data from the encoders 1220 to
coordinate activity. One or more microcontrollers provide system
configuration capability, in-system programmability for field
upgrade of firmware, and support for final data transmission
process.
An embodiment utilizes a matrixed configuration where a set of `n`
multi-view imaging systems are monitored by a group of `m` image
inspectors. In this configuration, as shown in FIG. 13, each
imaging system SYS.sub.1, SYS.sub.2, . . . SYS.sub.n is connected
to a network 1315 which provides a database 1305 for storage and
recall of all image data. A job scheduler 1310 keeps track of which
systems are online and of which operators INSPECT.sub.1,
INSPECT.sub.2, . . . INSPECT.sub.m are available for inspection.
Images from the database 1305 are transferred automatically to the
next available inspector for review. Inspection results are passed
back to the relevant imaging system which advantageously comprises
traffic control measures to direct manual search of suspect
vehicles or objects under inspection. System supervisor 1320 is, in
one embodiment, a manager who can monitor the state of the imaging
systems, monitor the efficiency of the operators and can
double-check inspection results from inspectors.
FIG. 14 shows deployment of multi-view imaging system to scan
cargo, in accordance with an embodiment of the present invention,
comprising a gantry 1400 with main imaging system (such as the
three-view system 400 of FIG. 4) at its center along with drive-up
and drive-down ramps 1410, 1411 respectively provided to allow
vehicles to pass through the centre of the inspection tunnel 1405.
In an alternate embodiment, the gantry 1400 is provided with a
conveyor to transport cargo through the inspection tunnel 1405. In
one embodiment, suitable tunnel sizes are up to 800 mm.times.500 mm
for small baggage, up to 1800 mm.times.1800 mm for packets and
small cargo, up to 3000 mm.times.3000 mm for small vehicles and
large cargo and up to 5500 mm.times.4000 mm for large vehicles and
containerized cargo.
FIG. 15 shows deployment of multi-view imaging system to scan
occupied vehicles in accordance with an embodiment of the present
invention, where vehicles in a multi-lane road 1500 approach a
plurality of scanners 1505, one scanner per lane. Vehicles 1525 are
scanned as they pass through respective scanners and approach a
plurality of corresponding traffic control systems 1510 such as
barrier or other suitable traffic control measures, including
traffic lights. Decision results from image inspectors are passed
automatically to these traffic control systems 1510 which then hold
or divert traffic as necessary. In an example illustration, a
holding area 1515 is shown with a vehicle 1520 parked therein as a
result of an inspector/operator marking scanned image of the
vehicle 1520 as suspicious.
In accordance with another aspect, the multi-view imaging system of
the present invention is deployed in the form of a mobile
inspection vehicle for rapid relocation to an inspection site. FIG.
16a shows mobile inspection system 1600 in its operating state
ready for scanning. Vehicle 1605 carries an embodiment of a
multi-view detection system, where a scanning tunnel 1610 is
surrounded by a set of booms 1615, 1621, 1622.
An exemplary boom stow sequence is graphically illustrated using
FIGS. 16b through 16g as follows:
FIG. 16b shows step 1650 comprising the folding up of vertical boom
1620 about a hinge point 1601 at the end of horizontal boom 1621.
This can be achieved, for example, by using a hydraulic cylinder
actuation although other mechanisms known to those of ordinary
skill in the art may be considered such as pull wires and
electronic drivers.
Step 1655, shown in FIG. 16c, comprises the simultaneous folding up
of horizontal boom 1621 and vertical boom 1620 about a hinge point
1602 which is positioned at the top of vertical support boom
1622.
Step 1660, shown in FIG. 16d, comprises lowering vertical support
boom 1622 toward the back of the vehicle 1605. Vertical support
boom 1622 may be folded down to a steep angle to allow room for an
operator inspection cabin to be co-located on the back of the
vehicle. In another embodiment, vertical support boom 1622 may be
folded down to be substantially parallel to the back platform of
the vehicle to allow a compact system configuration which is
advantageously developed to allow rapid re-location of systems
using conventional air transportation.
Step 1665, shown in FIG. 16e, comprises folding up the base section
1625 of the imaging system by at least 90 degrees from its
operating position. Thereafter, in step 1670, as shown in FIG. 16f,
comprises folding the outer horizontal base section 1625a of the
main base section 1625 by 180 degrees so that it lies parallel to
the inner base section 1625b.
Finally, in step 1675, shown in FIG. 16g a complete folding of the
base section occurs by a 90 degree rotation to complete system
stow. The aforementioned steps, 1650 through 1675, for boom
deployment to obtain operating state of FIG. 16a comprise boom stow
steps in reverse sequence.
In alternate embodiments, the mobile inspection system 1600 is
deployed with only the vertical and horizontal booms and not the
lower imaging section. This gives dual view imaging capability in
side-shooter configuration but no top-shooter view. In this mode,
the system is capable of full drive-by scanning mode with an
imaging configuration of at least one transmission view, with or
without backscatter capability.
The above examples are merely illustrative of the many applications
of the system of present invention. Although only a few embodiments
of the present invention have been described herein, it should be
understood that the present invention might be embodied in many
other specific forms without departing from the spirit or scope of
the invention. Therefore, the present examples and embodiments are
to be considered as illustrative and not restrictive, and the
invention may be modified within the scope of the appended
claims.
* * * * *